- The tree absorbs systemic insecticide by the roots or foliage. Its vascular system transports the insecticide throughout its cells and into its foliage. Every part of the tree contains traces of the insecticide, so the entire tree is afforded protection. Within two to four days after application the tree's system transports the toxin to all cells. When the unsuspecting caterpillar begins feeding on the tree's foliage, it inadvertently ingests the insecticide. The insecticide effectively kills the caterpillar.
- Systemic insecticides used to control caterpillars often contain imidacloprid, disulfoton or acephate. The homeowner can purchase systemic insecticides as foliar sprays or soil drenches. A tree service can drill several small holes into the trunk of the tree and inject the insecticide directly into the tree for faster uptake; unfortunately, the tree will suffer wounding, which can weaken it. Application of systemic insecticide must take place before the caterpillars hatch for the most effective control.
- Gypsy moth caterpillars and tent caterpillars cause heavy defoliation on oak trees along the eastern United States. The abundance of the caterpillars makes them a nuisance to humans. Arborists can inject systemic insecticides such as diflubenzuron or bendiocarb directly into the tree's trunk to control the caterpillars for up to one month, according to the Maryland Cooperative Extension. The tree's trunk may experience discoloration at the injection site.
- Unlike insecticidal sprays, systemic insecticides do not drift to surrounding trees and plant life. They pose no threat to animals or humans. Usually only leaf-chewing pests such as caterpillars are affected by the insecticides. Most insects will suffer no adverse effects. Unfortunately, bees appear to suffer from systemic insecticides because they gather the pollen and nectar of the tree's flowers. The insecticide-polluted pollen and nectar can damage or destroy the bees.
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